Car suspension system

ABSTRACT

In a car suspension system according to the present invention, a cylinder assembly comprises a cylinder housing and a rod fitted therein for axial reciprocation. An oil chamber and a gas chamber are defined inside the cylinder assembly, and the capacity of the gas chamber changes as the cylinder housing and rod reciprocate relative to each other. A damping force-generating mechanism is provided in the oil chamber. A metal bellows is contained in the cylinder assembly so as to be coaxial with the cylinder housing. The bellows can extend and contract in the axial direction of the cylinder housing. Having a sealed internal space, the bellows divides the oil and gas chambers completely. Thus, when the rod reciprocates in the axial direction, relative to the cylinder housing, the bellows extends and contracts axially.

BACKGROUND OF THE INVENTION

The present invention relates to a suspension system adapted to bearranged between members on the body side and wheel side of anautomobile, and more specifically, to an improvement of a suspensionsystem having an oil chamber and a gas chamber therein.

A prior art suspension system of an oil-gas pressure type comprises acylinder housing with a rod fitted therein. A gas chamber and an oilchamber are defined inside the cylinder housing. A high-pressure gas,such as nitrogen, is sealed in the gas chamber. Utilizing the repulsiveforce of the gas, the system serves as a gas spring. Dampingforce-generating means is provided inside the cylinder housing. As theoil in the oil chamber passes through the generating means, a dampingforce is produced by the viscous resistance of the oil, and is used todamp reciprocation of the rod.

Conventionally, a free piston is disposed between oil and gas, in orderto prevent the gas in the gas chamber from being absorbed into the oilin the oil chamber. In a suspension system disclosed in U.S. Pat. No.4,159,756, for example, a seal is provided on the outer peripheralsurface of a free piston.

In suspension systems using a free piston, however, considerablefrictional resistance occurs at the seal portion, as the piston moves.Moreover, the gas is liable to leak out through the seal portion of thepiston, so that it is thus difficult to completely prevent the gas frombeing absorbed into the oil.

An arrangement has been proposed such that the gas and oil chambers aredivided by means of a plastic partition member. However, the plasticmember cannot satisfactorily prevent gas permeation. Therefore,prolonged use of the suspension system may possibly cause a gas leak,thereby reducing the capacity of the gas chamber. If the gas chambercapacity lessens in this manner, the spring constant of the systemincreases. As a result, the car becomes less comfortable to ride in, andits ride height is lowered. Thus, a large gas leak makes it hard tomaintain the original performance of the suspension system. To cope withthis, gas must be resupplied or resealed into the gas chamber inside thecylinder housing. Resupply of gas, however, entails much trouble.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a carsuspension system, in which gas confined in a gas chamber, inside thesystem, can be securely prevented from being absorbed into oil in an oilchamber. Another object of the invention is to provide a suspensionsystem wherein a substantial frictional resistance such as is caused bythe use of a free piston, never occurs.

In order to achieve the above objects, a car suspension system accordingto the present invention comprises a cylinder assembly including atleast one cylinder housing and a rod, the rod being fitted in thecylinder housing and movable in the axial direction of the cylinderhousing, the cylinder assembly further including an oil chamber forcontaining oil and a gas chamber for containing gas; dampingforce-generating means disposed inside the cylinder assembly, andadapted to damp reciprocation of the rod by utilizing viscousresistance, produced when the oil in the cylinder assembly iscirculated; and a metal bellows located between the oil chamber and thegas chamber, so as to be coaxial with the cylinder housing, the bellowsbeing formed of a thin metal plate, having a sealed internal space,dividing the oil and gas chambers, and being capable of extending andcontracting in the axial direction of the cylinder housing.

In the suspension system constructed in this manner, if the rod moves inits contracting direction, relative to the cylinder housing, gas in thecylinder assembly is compressed. As a result, the capacity of the gaschamber is reduced, so that the gas contained therein increases in itsrepulsive force. If the rod moves in its extending direction, on theother hand, the capacity of the gas chamber increases, so that therepulsive force of the gas therein weakens.

Thus, as the cylinder housing and the rod reciprocate relatively in theaxial direction, the capacity of the gas chamber varies, so that themetal bellows extends and contracts. The oil and gas chambers arecompletely isolated from each other. Accordingly, the gas in the gaschamber can be securely prevented from being absorbed into the oil inthe oil chamber. Without the need to replenish the gas chamber,therefore, the spring characteristics and the ride comfort of the carcan be kept constant for a long time. By extending and contracting withthe variation of the capacity of the gas chamber, moreover, the bellowsnever produces such a substantial frictional resistance as is caused bythe movement of a free piston.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a suspension system accordingto a first embodiment of the present invention;

FIGS. 2 and 3 are sectional views showing modifications of part of a rodof the suspension system shown in FIG. 1;

FIG. 4 is a sectional view showing a modification of part of a metalbellows of the suspension system shown in FIG. 1;

FIG. 5 is a longitudinal sectional view of a suspension system accordingto a second embodiment of the invention;

FIG. 6 is a longitudinal sectional view of a suspension system accordingto a third embodiment of the invention;

FIG. 7 is a longitudinal sectional view of a suspension system accordingto a fourth embodiment of the invention; and

FIG. 8 is a longitudinal sectional view of a suspension system accordingto a fifth embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a first embodiment of the present invention. As is shown inFIG. 1, car suspension system 1 comprises cylinder housing 2 with rod 3fitted therein. Rod 3, having the shape of a hollow cylinder, canreciprocate along the axis of housing 2.

Cylinder housing 2 included cylindrical first member 2a with cylindricalsecond member 2b fitted therein. Mechanical seal 5, seal retainer 6, andsliding bearing 7 are attached to the upper end portion of second member2b. Sliding bearing 8 and rebound rubber 9 are attached to the lower endportion of second member 2b. Housing 2 and rod 3 constitute cylinderassembly 11.

Coupling member 12 is mounted on the lower end of cylinder housing 2.Housing 2 is connected to a member (not shown) on the wheel side, bymeans of the coupling member. Oil chamber 13 is defined inside housing2, and is filled with oil. Oil port 15 in housing 2 connects withchamber 13, so that oil for car height adjustment can be fed into ordelivered from chamber 13, through port 15. Cylinder housing 2 is formedwith hole 16, through which air leaks from housing 2 when oil isinjected therein. Hole 16 is closed by blind plug 17.

Coupling member 20 and bump rubber 21 are attached to the upper endportion of hollow rod 3, as is shown in FIG. 1. Dust cover 22 issituated between the outer end of rod 3 and cylinder housing 2. Cover 22surrounds a sliding surface of rod 3 which protrudes from housing 2.Damping force-generating mechanism 24 is attached to the inner end ofrod 3. It includes conventional plate valves 25 and 26.

Oil chamber 28 and gas chamber 29 are arranged in hollow rod 3. Chamber28 communicates with oil chamber 13 of cylinder housing 2 by means ofdamping force-generating mechanism 24. An inert gas, such as nitrogen,as a preferred example, is sealed at high pressure in chamber 29.

Metal bellows 31, having sealed internal space 30, is housed in hollowrod 3. It divides oil chamber 28 and gas chamber 29. In other words,space 30 of bellows 31 serves as gas chamber 29. The gas is fed intochamber 29 through gas-supply port 33. Port 33 is closed by blind plug34. A suitable quantity of liquid 35 is contained in bellows 31, wherebythe capacity of chamber 29 is adjusted. Bellows 31 is coaxial withcylinder housing 2, and can extend or contract in the axial direction ofhousing 2 and rod 3.

Metal bellows 31 is formed of a thin plate of stainless steel, forexample. The thickness of the plate is, for example, about 0.13 mm.Phosphor bronze, brass, aluminum, or any other suitable metal may beused in place of stainless steel. In this embodiment, bellows 31 isformed integrally from a cylindrical material, by plastic working.Alternatively, it may be formed by successively connecting a pluralityof bellows elements, in the axial direction, by means of welding.

As in a preferred modification of rod 3, part of which is shown in FIG.2, surface 37, in sliding contact with metal bellows 31, is coated withlow-friction layer 38. Layer 38 is formed of resin (e.g., ethylenetetrafluoride, nylon, etc.) which has a low coefficient of friction, andcannot be easily worn away. By using layer 38, the frictional resistancebetween bellows 31 and surface 37 is reduced, whereby bellows 31 isprevented from being worn away. Moreover, the sliding motion of bellows31 may be improved in smoothness by coating surface 37 with somelow-friction material other than resins. Alternatively, as is shown inFIG. 3, sleeve 39, formed of sintered metal material impregnated withoil, may be provided on surface 37 opposite bellows 31. In amodification shown in FIG. 4, metal bellows 31 is coated withlow-friction layer 38.

The operation of suspension system 1, constructed in this manner, willnow be described.

If rod 3 moves in a direction such that it is pushed into cylinderhousing 2, some of the oil in oil chamber 13 flows into oil chamber 28of rod 3, via damping force-generating mechanism 24. As the oil flowsthrough mechanism 24 in this manner, a damping force is produced by theviscous resistance of the oil. As a result, the motion of rod 3 issubjected to this resistance. At the same time, the gas in gas chamber29 is compressed in accordance with the depth of depression of rod 3.Accordingly, metal bellows 31 contracts, thereby reducing the capacityof chamber 29, so that the repulsive force of the gas increases.

If rod 3 moves in a direction such that it extends out from cylinderhousing 2, on the other hand, some of the oil in oil chamber 28 of rod 3flows into oil chamber 13 of housing 2. Also in this case, the oil flowspast damping force-generating mechanism 24, so that the motion of rod 3is damped. In response to the movement of rod 3 in the extendingdirection, moreover, gas chamber 29 increases its capacity, so thatmetal bellows 31 extends.

Thus, as rod 3 repeatedly extends and contracts relative to cylinderhousing 2, the suspension system serves both as a shock absorber and agas spring. Moreover, the axial position or the length of projection ofrod 3, relative to housing 2, can be changed by delivering the oil intoor from oil chamber 13 through oil port 15. Thus, the ride height of thecar can be changed.

In suspension system 1, oil chamber 28 and gas chamber 29 are completelyisolated from each other by metal bellows 31, so that the gas in chamber29 can be securely prevented from being absorbed into the oil in chamber28. Without the need to replenish chamber 29 with gas, therefore, thespring characteristics and the ride comfort of the car, in the earlystages of use, can be maintained for a long time. Also, the springconstant can be adjusted by controlling the quantity of liquid 35 inbellows 31, to change the capacity of gas chamber 29.

FIG. 5 shows a second embodiment of the present invention. Suspensionsystem 1 of this embodiment comprises second cylinder housing 41, inaddition to first cylinder housing 2. In the following description ofthe second embodiment, like reference numerals are used to designatelike portions as in the first embodiment, for simplicity ofillustration. Only differences between the two embodiments will now bedescribed specifically.

Oil chamber 28' and gas chamber 29' are arranged in second cylinderhousing 41. The two chambers are divided by metal bellows 31, which hassealed internal space 30. In the second embodiment, chambers 28' and 29'are defined inside and outside bellows 31, respectively. A suitablequantity of liquid 35 is contained in housing 41, whereby the capacityof gas chamber 29' is adjusted. Oil chamber 28' communicates with oilchamber 28 inside hollow rod 3, by means of passage 42.

Inner cylinder 44 is provided inside second cylinder housing 41. Metalbellows 31 is located between cylinder 44 and housing 41, so as to becoaxial with housing 41. Bellows 31 can extend and contract in the axialdirection of housing 41. Preferably, low-friction layer 38, as shown inFIG. 2, or oil-impregnated metal sleeve 39, as shown in FIG. 3, may beprovided on inner peripheral surface 41a of housing 41 and/or outerperipheral surface 44a of cylinder 44. Alternatively, bellows 31 may becoated with low-friction layer 38, on either of its outer and innerperipheral surfaces, as is shown in FIG. 4.

When rod 3 reciprocates in the axial direction, relative to firstcylinder housing 2, oil flows between oil chamber 13 inside housing 2and oil chamber 28' inside second cylinder housing 41, via passage 42and oil chamber 28 inside rod 3. Thus, the oil flows through dampingforce-generating mechanism 24, and a damping force is produced by theviscous resistance of the oil. As rod 3 extends and contracts, moreover,the capacity of gas chamber 29' varies, and metal bellows 31 extends andcontracts. Also in this embodiment, oil and gas chambers 28' and 29' aredivided completely from each other by bellows 31, so that gas in chamber29' can be prevented from being absorbed into the oil in chamber 28'.

FIG. 6 shows a third embodiment of the present invention. In thisembodiment, the relative positions of metal bellows 31 and innercylinder 44 are opposite to those in the case of the second embodiment(FIG. 5). Gas chamber 29' and oil chamber 28' are defined inside andoutside bellows 31, respectively. Since the second and third embodimentshave no substantial differences, like reference numerals are used todesignate like portions in the two embodiments, for simplicity ofillustration.

FIG. 7 shows a fourth embodiment of the present invention. In thisembodiment, second cylinder housing 41 is inverted, as compared with thearrangement of the second embodiment. Damping force-generating mechanism24 is provided inside housing 41. Passage 42 is located between oilchamber 13 in first cylinder housing 2 and oil chamber 28' in housing41.

In the fourth embodiment constructed in this manner, when rod 3 moves inthe axial direction, relative to first cylinder housing 2, oil flowsbetween oil chambers 13 and 28', via damping force-generating mechanism24. As the oil flows in this manner, the capacity of gas chamber 29'changes, so that metal bellows 31 extends and contracts. As regardsother portions, the fourth embodiment has the same arrangement andfunctions as the second or third embodiment.

In the second, third, and fourth embodiments described above, passage 42can be provided within one end portion of rod 3 or second housing 41.Alternatively, passage 42 can be made of a pipe connecting rod 3 andsecond housing 41. Furthermore, two or more housings 41 can be providedin each of the second, third, and fourth embodiments.

FIG. 8 shows a fifth embodiment of the present invention. In thedescription to follow, like reference numerals are used to designatelike portions as in the first embodiment, for simplicity ofillustration.

In the fifth embodiment, cylinder housing 2 includes shorter-diameterlower portion 2c and longer-diameter upper portion 2d. Metal bellows 31is contained in portion 2d, so as to be coaxial with housing 2. Thelower end of bellows 31 is fixed to housing 2 by means of bellows-fixingmember 50. Bellows 31 can extend and contract in the axial direction ofhousing 2.

Metal bellows 31 includes bellows body 51, capable of extending andcontracting in the axial direction of cylinder housing 2, and lid 52fixed to an open end of body 51. The bellows body, like that of metalbellows 31 of the first embodiment, is formed of a thin metal plate.Since lid 52 is welded in a liquid-tight manner to the open end of body51, sealed internal space 30 is defined inside bellows 31. Fittingportion 54, having seal 53 thereon, is formed on the inner surface oflid 52. The lower end of bellows body 51 is welded to bellows-fixingmember 50. Member 50 is fixed to the boundary between shorter- andlarger-diameter portions 2c and 2d of cylinder housing 2. Seals 55 and56, such as O-rings, are provided on the inner and outer peripheralsurfaces of member 50, respectively.

Oil chamber 28 and gas chamber 29 are defined inside cylinder housing 2.The two chambers are divided by metal bellows 31. Inner cylinder 60 issituated inside housing 2, so as to be substantially coaxial withhousing 2 and bellows 31. The lower end of cylinder 60 is fixed tohousing 2 by welding or the like. Cylinder 60 is formed with oil holes61. Also, the inner cylinder is provided, at its upper end, with openingportion 60a of a size large enough to receive fitting portion 54 of lid52. Opening portion 60a is adapted to engage seal 53 on fitting portion54 when bellows body 51 is contracted to a predetermined degree or more.

Oil chamber 28 inside metal bellows 31 is filled with oil. Itcommunicates with oil port 15 by means of the inside of inner cylinder60, damping force-generating mechanism 24, and oil holes 61. Hydraulicunit 63 is connected to port 15. In this embodiment, unit 63 includeshydraulic source 64. Arranged between source 64 and port 15 aresolenoid-operated valve 65 for lifting and check valve 66 for car-heightmaintenance. Solenoid-operated valve 68 for lowering is situated betweenoil tank 67 and port 15.

Gas is sealed, under high pressure, in gas chamber 29, which is definedbetween the outer surface of metal bellows 31 and the inner surface ofcylinder housing 2. The gas is fed into chamber 29 through gas-supplyport 33. If oil port 15 is connected to tank 67, when sealing the gasinto chamber 29, bellows 31 is urged to contract to the limit bygas-sealing pressure, despite the presence of the oil in oil chamber 28.When bellows 31 has contracted to the predetermined degree or more,however, fitting portion 54 of lid 52 comes into close contact withopening portion 60a of inner cylinder 60. As a result, bellows 31 isprevented from contracting further. At the same time, the oil isconfined to a gap between bellows body 51 and cylinder 60. Thus, eventhough the pressure of the gas, fed through port 33, is relatively high,body 51 can be prevented from being severely deformed. Accordingly, body51 may be relatively low in mechanical strength, that is, it can bereduced in thickness.

In this embodiment, rod 3 is solid. It can reciprocate in the axialdirection, relative to cylinder housing 2. Sliding bearing 7 is providedbetween the sliding surfaces of housing 2 and rod 3. Low- andhigh-pressure seals 70 and 71 are arranged close to bearing 7. Drainpipe 72 is connected between seals 70 and 71. Communicating with tank67, pipe 72 allows the oil to leak out from seal 71. Therefore, seal 71requires only a small clamping force, so that the sliding resistance ofrod 3 on cylinder housing 2 is lowered.

Distal end portion 3a of rod 3, which is piston-shaped, penetrates intometal bellows 31. Damping force-generating mechanism 24 is attached toportion 3a. In this embodiment, mechanism 24 has disk-shaped valve body75 mounted on the tip end of body portion 3b of rod 3. Sliding bearing76 is fitted on the outer peripheral surface of body 75, in slidingcontact with inner cylinder 60. Thus, rod 3 is supported stably by twosliding bearings 7 and 76 which are spaced in its axial direction.

Disc-shaped valve body 75 has oil passage 77 extending in its axialdirection. Relief plate 78 is provided at one end side of passage 77,and opens when rod 3 moves in its extending direction. Normally, plate78 is urged in a closing direction by coil spring 79. Relief plate 80 isprovided at the other end side of passage 77, and opens when rod 3 movesin its contracting direction. Further, member 82 with constant orifice81 is fixed to the tip end of rod body 3b.

The operation of the fifth embodiment with the above construction willnow be described.

If rod 3 moves in its extending direction, relative to cylinder housing2, oil inside inner cylinder 60 passes through damping force-generatingmechanism 24, thereby producing a damping force. At the same time, thecapacity of gas chamber 29 increases by a volume corresponding to thelength of extension of rod 3, and bellows body 51 contractscorrespondingly.

If rod 3 moves in its contracting direction, on the other hand, the oilflows through damping force-generating mechanism 24, thereby producing adamping force. Also, gas chamber 29 is compressed by a volumecorresponding to the depth of depression of rod 3, and bellows body 51extends correspondingly. Thus, the gas in chamber 29 is compressed,thereby increasing its repulsive force.

The oil can be delivered into or from cylinder housing 2 by operatingsolenoid-operated valve 65 or 68 of hydraulic unit 63. By changing thequantity of oil in housing 2, in this manner, the length of extension ofrod 3 relative to housing 2, that is, the ride height of the car, can beadjusted.

According to the fifth embodiment, as described above, inner cylinder 60and distal end portion 3a of rod 3 penetrate metal bellows 31. If endportion 3a of rod 3 moves toward lid 52 or in the contracting direction,bellows 31 extends so as to move away from portion 3a. In other words,internal space 30 of bellows 31 serves not only to contain the oil, butalso to receive rod 3 effectively. Even though bellows 31 is containedin cylinder housing 2, therefore, the overall length of cylinderassembly 11 can be relatively short.

Further, distal end portion 3a of rod 3 is supported by sliding bearing76, and the middle portion of rod 3, with respect to its axialdirection, is also supported by sliding bearing 7. Since the distancebetween bearings 7 and 76 can be made long enough, the axialreciprocation of rod 3 is stable, and the sliding resistance isrelatively small. Hydraulic unit 63 and drain pipe 72 may be omitted.

Instead of being fixed to cylinder housing 2, moreover, inner cylinder60 may be formed integrally with rod 3. In this case, cylinder 60 isslidably supported with the use of a sliding bearing attached to bellowsfixing member 50. Alternatively, a sliding bearing (not shown) may beattached to member 50 so as to support rod 3, without the use ofcylinder 60.

In contrast with the arrangement of the fifth embodiment, furthermore,the system may be inverted so that coupling members 12 and 20 of rod 3and cylinder housing 2 are connected to the car-body side and wheelside, respectively. Alternatively, an actuator, such as a pulse motor,may be contained in rod 3 so that the opening area of the orifice ofdamping force-generating mechanism 24 is controlled by means of theactuator. With this arrangement, the damping force can be changed inaccordance with the road surface conditions or running conditions.

What is claimed is:
 1. A suspension system used in a car, comprising:acylinder assembly including at least one cylinder housing and a rod, thecylinder housing including a smaller-diameter portion and an adjacent,coaxially aligned larger-diameter portion, said rod being fitted in thecylinder housing and being movable in the axial direction of thecylinder housing, said cylinder assembly further including an oilchamber containing oil and a gas chamber containing gas which provides aspring force; damping force-generating means disposed inside thecylinder assembly, and adapted to damp reciprocation of the rod byutilizing viscous resistance, produced when the oil in the cylinderassembly is circulated, comprising: a hollow inner cylinder having anopen end, and being substantially coaxial with the cylinder housing,said inner cylinder being disposed inside the oil chamber of saidcylinder housing and extending from within the smaller diameter portionto within the larger diameter portion of the cylinder housing, saidhollow inner cylinder having a first oil chamber therein, and defining asecond oil chamber in an annular space formed between said hollow innercylinder and the smaller-diameter portion of the cylinder housing, saidfirst and second oil chambers being in communication with each otherthrough an opening in the inner cylinder; a piston mounted at the end ofthe rod, and located in the inner cylinder such that the inner cylinderis divided into two oil containing regions one of which includes saidfirst oil chamber, the piston having orifices; a metal bellows locatedbetween the oil chamber and the gas chamber of the cylinder assembly, soas to be substantially coaxial with the cylinder housing, said bellowsbeing formed of a thin metal plate dividing the oil and gas of thecylinder assembly, and being capable of extending and contracting in theaxial direction of the cylinder housing, said bellows being disposedbetween an inner peripheral surface of only the larger-diameter portionof the cylinder housing and an outer peripheral surface of the innercylinder, said metal bellows having a lid located opposite the open endof the inner cylinder, the lid having seal means so as to be fitted onsaid open end, in a liquid-tight manner, when the bellows is contractedto a predetermined degree; and hydraulic means connected to saidcylinder assembly for delivering oil into or out of the oil chambers. 2.The suspension system according to claim 1, wherein said cylinderhousing has a stepped section between the smaller-diameter portion andthe larger-diameter portion, and the stepped section receives abellows-fixing member, said bellows being fixed at an end thereof bymeans of the bellows-fixing member.
 3. The suspension system accordingto claim 1, wherein said open end of said inner cylinder is located insaid larger-diameter portion of said cylinder housing.
 4. The suspensionsystem according to claim 1, wherein said metal bellows is formed of athin, single-layer metal plate.